This invention relates generally to imaging systems and, more particularly, to a phantom for use in evaluating substance scoring using imaging system-generated images.
Imaging systems include a source that emits signals (including but not limited to x-ray, radio frequency, or sonar signals), and the signals are directed toward an object to be imaged. The emitted signals and the interposed object interact to produce a response that is received by one or more detectors. The imaging system then processes the detected response signals to generate an image of the object.
For example, in computed tomography (CT) imaging, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the xe2x80x9cimaging planexe2x80x9d. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third-generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a xe2x80x9cviewxe2x80x9d. A xe2x80x9cscanxe2x80x9d of the object comprises a set of views made at different gantry angles during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two-dimensional slice taken through the object.
One method for reconstructing an image from a set of projection data is referred to in the art as the filtered backprojection technique. This process converts the attenuation measurements from a scan into integers called xe2x80x9cCT numbersxe2x80x9d or xe2x80x9cHounsfield unitsxe2x80x9d, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
To reduce the total scan time required for multiple slices, a xe2x80x9chelicalxe2x80x9d scan may be performed. To perform a xe2x80x9chelicalxe2x80x9d scan, the patient is moved while the data for the prescribed number of slices is acquired. Such a system generates a single helix from a one-fan-beam helical scan. To further scan time, multi-slice helical scans can also be used. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed. In addition to reduced scanning time, helical scanning provides other advantages such as imaging at any location, reduced dose, and better control of contrast.
It is known to use imaging data to identify evidence of certain diseases by detecting and quantifying, i.e., xe2x80x9cscoringxe2x80x9d, substances that may be present in a patient""s system. One known software system, for example, analyzes CT images of the heart to quantify amounts of calcium in coronary regions of interest. Scoring is based upon the volume and Hounsfield unit of a calcified region. A number called the xe2x80x9ccalcium scorexe2x80x9d expresses the quantity of calcium present in the patient""s arterial system.
It would be desirable to provide a system and method for verifying accuracy of substance-scoring systems. It also would be desirable to provide a system and method for measuring the validity, reproducibility and repeatability of a substance score for different imaging systems (e.g. CT single-slice or multi-slice), for different scanning methods (e.g. CT helical or axial), and for different image reconstruction algorithms.
Co-pending application Ser. No. 09/541,147, filed Mar. 31, 2000, discloses a preferred phantom which simulates a heart with calcium deposits and related method that are usable in this manner. It is possible to use the phantom described Ser. No. 09/541,147 as either a static (non-moving) or dynamic (moving) phantom, inasmuch as disclosed phantom is robust and can be used either way. Dynamic phantoms are desirable because a human heart continues pumping during imaging operations, and therefore a dynamic phantom provides a better simulation of the human heart. Therefore, it would be desirable to provide a phantom and method in which the phantom is capable of moving, especially a phantom and method in which the phantom is capable of moving in a manner that simulates pumping of a human heart.
According to a first preferred aspect, a method of evaluating a substance scoring system comprises acquiring data from a phantom using an imaging system, moving at least a portion of the phantom during the acquiring step, and generating an actual substance score for the phantom based on the data acquired using the imaging system. The phantom simulates a human organ such as a human heart. The phantom is provided with a motion profile that simulates a motion profile of the human organ.
According to a second preferred aspect, a system comprises a phantom, a movable phantom holder, and an imaging system. The phantom includes a core and a plurality of volumes embedded in the core. Each of the plurality of volumes has an imaging number that simulates a substance of interest, with different ones of the plurality of volumes having different imaging numbers that simulate different concentrations of the substance. The phantom is mounted to the movable phantom holder, which causes the phantom to move. The imaging system generates an actual substance score, which expresses a quantity and a concentration of the simulated substance present in the phantom.
The above-described phantom and method allow a scoring system user to verify substance scoring accuracy and to compare scores resulting from different imaging systems, scanning methods and reconstruction algorithms during motion of the simulated organ.